The invention relates to magnetic transducers suitable for use in connection with narrow track recording and/or reproducing and, particularly, where severe operating stresses are encountered.
Ferrite materials are widely used in magnetic recording for their preferred electrical and magnetic characteristics, as well as their resistance to wear. This latter feature is particularly advantageous in magnetic heads which are subjected to the abrasive effects of contacting magnetic recording media. However, ferrite material is not suitable for heads that are likely to encounter severe operating stresses or heads for narrow track recording applications because of its inherent brittleness. Ferrite heads encountering severe operating stresses, for example, when used in rotary head equipment where high relative speeds between the head and contacting recording medium are common, frequently chip and often structurally fail. In addition, narrow track ferrite heads chip easily during the manufacturing process.
The problem of manufacturing narrow track ferrite magnetic heads is described, e.g., in U.S. Pat. No. 3,813,693 to Gooch et al. That patent teaches forming glass pockets about the transducing gap area of the head. The pockets isolate the weak edges of the ferrite core forming the magnetic transducing gap. Thus, the gap area is protected from the forces creating the severe operating stresses and causing chipping and erosion of the ferrite material. Such heads have a rather complicated design and the method of building them is not practicable for track widths under 5 mils.
In another type of prior art narrow track ferrite head utilized in rotary scan magnetic tape recorders, the opposite side walls defining the transducing gap width are notched to the desired gap width dimension. This head has a core approximately 0.010 inches wide which is notched down to approximately 0.005 inches. However, below this dimension the structural strength of the head suffers and may fail under the stress of running against the tape at a high relative speed. In some cases, the notch causes the formation of an undesirable air bearing between the relatively moving head and tape, which results in the head undesirably flying above the tape.
Another prior art magnetic transducer is described in the U.S. Pat. No. 3,303,292 to Bedell et al. According to the teachings of that patent, a metallic (Alfesil) magnetic core is attached on one side to a nonmetallic (ferrite) magnetic body. The Alfesil core defines the nonmagnetic transducing gap of the transducer and the ferrite body provides a low reluctance path by shunting the rear portion of the Alfesil core. This transducer design is not suitable for applications where narrow track, wear resistant transducers are required. Furthermore, it does not provide the structural support and protection against gap erosion necessary for narrow track heads made of inherently brittle and porous magnetic material, which heads are intended for use in applications where high relative transducer to recording medium speeds are likely to be encountered, such as in rotary head recording equipment.
Another prior art method of batch fabrication of multitrack magnetic heads suitable for narrow track application is described in the U.S. Pat. No. 3,613,228 to Cook et al. According to this method, multiple face parts of the magnetic heads are manufactured by glass-bonding a magnetic ferrite block to a nonmagnetic block and by lapping it to a thickness corresponding to a desired track width. A multiplicity of these blocks having alternative layers of magnetic and nonmagnetic material is stacked and glass-bonded together. The stack is then cut into sections containing these alternative layers and each two sections are glass-bonded together to form a face part having a transducing gap between two adjacent ferrite layers. The face part is then glass-bonded to a back core containing coils in grooves. While this method is useful for batch fabrication of multigap, narrow track head assemblies, such as for fixed head disc files, it is not suitable for manufacturing a high quality transducer intended for operating under severe stresses, such as encountered in rotary head recording equipment, due to high relative speeds between the transducer and recording medium.